Known devices for the coating of running paper or cardboard webs have a coating mechanism swingable towards the web in the area where it wraps about the counter-roller and apply an excess of coating material e.g. coating paint. This portion of the mechanism is followed in the running direction of the web by a dosage system with a dosing element (e.g. a doctor blade) which wipes the excess off, down to the desired coating level.
From DE 39 16 620-A1 (Corresponding to U.S. Pat. No. 5,117,767) describes a device of this kind is known wherein the coating mechanism comprises an application roller drawing liquid from a liquid chamber and which is swingably supported with respect to the counter-roller. In the working position a narrow clearance (coating gap) is left between the coating roller and the counter-roller, this gap being completely filled by the provided coating paint. The coating mechanism can be swung away into a servicing position for maintenance, e.g. cleaning.
The dosing system comprises a doctor beam swingable towards the counter-roller with a doctor blade as a dosing element which can be pressed against the web supported by the counter-roller with an adjustable pressure and at a preselected angle, for the purpose of dosing the weight of the coating. The doctor beam with the dosing element can also be swung into a servicing position, e.g. for replacement of the doctor blade.
In a high-speed coating installation (web speed&gt;600 m/min) it is required to swing the coating mechanism and/or the dosing system quickly and accurately in the respective working position at the counter-roller. It is also often necessary to swing the coating or dosing mechanism away very quickly from the respective working position, e.g. for instance when it passes a joint with a web splice, or in the case of defective spots or in the case of a web break. If the coating mechanism as well as the dosing system are supposed to be swung back and forth quickly, it becomes necessary to precisely coordinate the timing of the two swinging motions. On the one hand it has to be prevented that an undosed paint film is applied which would contaminate subsequent installation parts and soften and weaken the web, with the consequence of breaks in the web. On the other hand, a doctor blade should only be pressed against a dry web for a short period of time, because otherwise it can heat up and burn out due to high friction.